From fungal diversity to antimicrobial innovation: the potential of biotransformation in the era of resistance.

Antimicrobial resistance (AMR) continues to outpace the development of new anti-infective agents, particularly against priority bacterial pathogens such as Acinetobacter baumannii, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Staphylococcus aureus, as well as clinically relevant fungi including Candida auris. In this scenario, biotransformation has emerged as a complementary innovation strategy for antimicrobial discovery because it expands the chemical space around bioactive scaffolds through selective enzymatic or whole-cell modification. Among the available biocatalysts, fungi are especially attractive due to their metabolic plasticity and broad enzymatic repertoire, including cytochrome P450 monooxygenases, unspecific peroxygenases, laccases, peroxidases, and hydrolases. Current evidence shows that fungal systems can mediate regio- and stereoselective transformations of xenobiotics, aromatics, steroids, terpenes, and lipids, generating structurally refined metabolites of pharmacological and biotechnological interest. This narrative review discusses where fungal biotransformation currently stands as a platform for antimicrobial innovation, highlighting representative enzyme-characterized examples, the main fungal groups and catalytic systems involved, and the experimental workflows used to evaluate these processes. Particular emphasis is given to assay design with growing cells, resting cells, and isolated enzymes, as well as to analytical monitoring by time-course sampling, LC-HRMS/MS, dereplication, molecular networking, isolation, and structural elucidation. Overall, fungal biotransformation is presented as a discovery-enabling platform that links biodiversity, enzymatic catalysis, analytical chemistry, and biological prioritization in the search for new anti-infective molecules.